The present invention relates to an apparatus and method for driving a fuel injector. In particular, the invention relates to an apparatus and method for controlling the quantity and rate of fuel to be injected into an internal combustion engine.
Fuel injectors typically use a solenoid that controls an armature. When a current is applied to the solenoid, a magnetic field is created, which raises the armature against spring and fuel pressure forces, and allows fuel to flow. When the current is removed, the armature returns to a closed position by the bias of the spring and fuel flow is terminated. Fuel injector opening time and closing time are important parameters in fuel injection strategies. Short opening and closing times create a longer linear flow range. A longer linear flow range results in lower idle speed, improved idle stability, fuel savings on deceleration, more precise fuel control at low loads, and hydrocarbon emission reduction. Prior methods of shortening injector response time have attempted to reduced the electrical resistance in the solenoid coil or increase the voltage applied to the solenoid. Lower resistance in the given size coil, however, results in less magnetic force, reducing the effectiveness of the solenoid. Increasing voltage requires the use of a DCxe2x80x94DC converter, increasing costs. Furthermore, the higher voltage creates and dissipates more heat into the local electronics. Therefore, the device cannot be integrated into other electronic devices.
Other devices have pre-charged (or pre-magnetized) the solenoid with a current that is below the current that can move the armature. This pre-charging current reduces the time required for the current in the solenoid to increase to an opening level. Some devices apply a constant, low-level current to the solenoid. This strategy reduces opening time, but it also reduces the effective spring closing force, hence increases the possibility of false opening due to high backpressure during combustion and leakage. This strategy requires high energy consumption. Other pre-charging devices do not apply a continuous current, but instead apply a pre-charging current for a limited time before opening. These devices often require expensive circuitry for a closed-loop control of the pre-charging current and are not optimized to minimize current use. Therefore, a fast, inexpensive device and method are required to minimize opening time and reduce energy consumption without some of the shortcomings described above.
In one embodiment of the invention, a voltage source is provided. The voltage source is electrically connected to a drive circuit for limiting the current from the voltage source to an injector solenoid. An engine controller is connected to the circuit and dictates the timing and duration that the circuit performs for each injector. The circuit determines the current-limiting waveform of the injector solenoid. When the driving voltage pulse is sent to the solenoid coil, current begins to build up in the coil and creates a magnetic field. An armature is located inside the injector as a part of the solenoid magnetic circuit and has a thin axial air gap to the rest part of the solenoid magnetic circuit. The armature moves toward the counterpart pole face to close the air gap in response to the magnetic flux. The armature movement dictates the injector needle valve lift that controls the amount of fuel that flows into the internal combustion engine. When a magnetic flux is not applied, a spring keeps the armature in a closed position, preventing fuel flow.
In a second embodiment of the invention, a method of controlling a current in a solenoid coil to move an armature in a fuel injector is provided. The method applies a pre-charging current at a level that does not move the armature for a period until the pre-charging current level is achieved and stabilized. The method then applies a valve-opening current that is greater than the pre-charging current and has an upper limit sufficient to fully move said armature. Next, a valve-holding current is applied that is less than the valve-opening current and the pre-charging current but just sufficient to keep the armature in fully open position. Finally, all current is removed, allowing the armature to close.
In another embodiment of this invention, various means are provided for applying a pre-charging current, a valve-opening current, and a holding current to the armature and solenoid assembly.
Other systems, methods, features, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.